Francisco Bosch Reig

H-point standard additions method. Part 1. Fundamentals and application to analytical spectroscopy

A modification of the standard additions method called the “H-point standard additions method” is proposed in order to obtain an unbiased analyte concentration when both analyte and interferents are present in a sample. It also permits the determination of an interferent known to be present. The method uses the analytical signal data at two selected wavelengths, giving two straight lines that have a common point with coordinates H (–CH, AH), where –CH is the unknown analyte concentration and AH the analytical signal due to an interferent. Examples of the application of the proposed method are given.

Spectrophotometric analysis of mixtures of two components with extensively or completely overlapping spectra by the H-point standard additions method

SummaryThis paper discusses the requirements and scope of application of the H-Point Standard Additions Method (HPSAM) for resolving binary mixtures. Various mixtures of dyes with extensively or completely overlapping spectra were assayed with accurate, precise results. The method thus developed was also applied to the spectrophotometric resolution of binary mixtures of phenol and o-cresol, the absorption bands of which lie in similar positions and feature similar absorptivities.

Application of the H-point standard additions method by using absorbance increment values as analytical signals

This paper demonstrates how the absorbance increment (DeltaA) between two wavelengths selected according to the fundamental criteria for application of the H-Point standard additions method (HPSAM) are only related to the analyte concentration. A procedure for calculation of the unknown analyte concentration with no bias error by applying HPSAM to DeltaA values in much the same way as the method of standard additions (MOSA), is reported. The method was also applied to a calibration with a single standard. The results obtained on 6 samples with maximal separations between 65 and 0 nm are reported. Finally, the proposed method was applied to the resolution of different phenol-o-cresol mixtures.

Determination of amphetamine and methamphetamine in urine with sodium 1,2-naphthoquinone 4-sulphonate using the H-point standard addition method

Abstract The determination of amphetamine and methamphetamine in urine by the H-point standard additions method (HPSAM) is described. An extraction-spectrophotometric method for the determination of these drugs with sodium 1,2-naphthoquinone 4-sulphonate using n-hexane-ethyl acetate (1:1) as the extraction solvent is proposed. The analytes are previously extracted into n-hexane. Although their spectra are very similar and overlap, the H-point standard additions method provides good results for both amines. The applicability of the method when the total Youden blank is present is demonstrated. The relative errors found were less than 10%.

Determination of fluoride after direct separation from acid medium by collection of its volatile compounds

A method is proposed for determination of fluoride by separation in acid medium followed by ion-selective electrode measurement. The separation is done at temperatures up to 200 °C, without any previous treatment of the sample, in a PTFE reactor designed to ensure the complete absorption of volatile fluoride compounds. The distillation variables (temperature, time and acid concentration) have been optimized and the interference of other various species in the separation step has been studied. The method has been applied to geological samples. The results obtained are statistically satisfactory.

Quantitative study of a selectivity index applicable to spectrophotometric methods of analysis

A selectivity index has been developed that quantifies the selectivity of various spectrophotometric methods of analysis. This has been produced by considering the interaction between the analyte and interferent and developing an algorithm to calculate the value of the index in each instance. The expression obtained has been applied to practical examples.